Differential excretion of urinary proteins in children with vesicoureteric reflux and reflux nephropathy

We studied 40 children with a history of vesicoureteric reflux (VUR) without evidence of renal scarring, 93 children with a history of VUR and renal scarring and 10 children with previous urinary tract infections in whom the urinary tract was radiologically normal. Urine retinol-binding protein (RBP), albumin and N-acetyl-beta-D-glucosaminidase (NAG) were measured in each child. All were free from infection at the time of the analysis. Urinary RBP and NAG levels were significantly elevated (P < 0.001) in the group of children with renal scarring. Elevated RBP levels were detected in 51% of children with bilateral renal scarring compared with 7% of children with unilateral scarring. Urine RBP excretion increased progressively according to the type of scarring, best determined by the type of scarring of the less affected kidney. In children with renal scarring, elevated NAG levels were seen mostly in the 65 children with bilateral scarring and severe reflux. Urine albumin excretion was elevated in 10 children, 9 with bilateral scarring, all of whom had elevated RBP excretion. Urine protein excretion was unaffected by the presence or absence of persisting VUR. There was a strong negative correlation between glomerular filtration rate and RBP excretion (r = -0.69). We conclude that evidence of tubular dysfunction is common in children with bilateral renal scarring and usually precedes any glomerular protein leak. Tubular dysfunction may be the consequence of relative nephron hyperperfusion in the presence of bilateral scarring.